Line Follower Robot

Building a PID Line Follower Robot with Arduino

Line Follower Robot

In this tutorial, we'll build a more intelligent and smooth line follower robot using PID control. Instead of making hard turns or reacting late, a PID-controlled robot adjusts motor speeds dynamically to stay on track with precision.

🔍 What is PID Control?

PID stands for Proportional, Integral, and Derivative. It’s a control system algorithm used in robotics to reduce error:

• P (Proportional): Reacts to how far off the robot is from the line
• I (Integral): Accumulates past error (optional here)
• D (Derivative): Reacts to how quickly the error is changing

This method provides smoother motion and higher accuracy compared to simple conditional logic.

🧰 Components Required

• Arduino Uno/Nano
• L293D or L298N Motor Driver
• BO Motors with Wheels (x2)
• IR Sensors (x3) – Left, Center, Right
• Chassis and Power Supply (7.4V–12V)
• Jumper Wires and Battery Holder

🔌 Circuit Diagram

Line Follower Robot Circuit Diagram

🔗 Pin Mapping (Example)

• Motor A: IN1 = 7, IN2 = 6, ENA = 9
• Motor B: IN3 = 5, IN4 = 4, ENB = 10
• IR Sensors: Left = 3, Center = 8, Right = 2

💻 Arduino PID Code

Copy and upload the code below to your Arduino:

// Motor pins
const int in1 = 7, in2 = 6;
const int in3 = 5, in4 = 4;
const int ena = 9, enb = 10;

// IR sensor pins
const int irl = 3;
const int irc = 8;
const int irr = 2;

// PID constants
float Kp = 25;
float Ki = 0;
float Kd = 15;

int baseSpeed = 120;
int maxSpeed = 255;

float error = 0;
float previousError = 0;
float integral = 0;

void setup() {
  pinMode(in1, OUTPUT); pinMode(in2, OUTPUT);
  pinMode(in3, OUTPUT); pinMode(in4, OUTPUT);
  pinMode(ena, OUTPUT); pinMode(enb, OUTPUT);
  pinMode(irl, INPUT); pinMode(irc, INPUT); pinMode(irr, INPUT);
}

void loop() {
  int left = digitalRead(irl);
  int center = digitalRead(irc);
  int right = digitalRead(irr);

  if (left == 0 && center == 1 && right == 1) error = -1;
  else if (left == 0 && center == 0 && right == 1) error = -0.5;
  else if (left == 1 && center == 0 && right == 1) error = 0;
  else if (left == 1 && center == 0 && right == 0) error = 0.5;
  else if (left == 1 && center == 1 && right == 0) error = 1;
  else if (left == 0 && center == 0 && right == 0) error = 0;
  else {
    stopMotors();
    return;
  }

  integral += error;
  float derivative = error - previousError;
  float correction = Kp * error + Ki * integral + Kd * derivative;
  previousError = error;

  int leftSpeed = constrain(baseSpeed - correction, 0, maxSpeed);
  int rightSpeed = constrain(baseSpeed + correction, 0, maxSpeed);

  moveForward(leftSpeed, rightSpeed);
}

void moveForward(int lSpeed, int rSpeed) {
  digitalWrite(in1, HIGH); digitalWrite(in2, LOW);
  digitalWrite(in3, HIGH); digitalWrite(in4, LOW);
  analogWrite(ena, lSpeed); analogWrite(enb, rSpeed);
}

void stopMotors() {
  digitalWrite(in1, LOW); digitalWrite(in2, LOW);
  digitalWrite(in3, LOW); digitalWrite(in4, LOW);
  analogWrite(ena, 0); analogWrite(enb, 0);
}

📏 PID Tuning Tips

• Start with: Kp = 25, Ki = 0, Kd = 15
• If it wobbles too much, increase Kd
• If it reacts too slowly, increase Kp
• Leave Ki at 0 unless you see long-term drift

🧪 Testing

Place the robot on a dark line over a light surface. It should track the line smoothly, adapting dynamically on curves. If not, recheck sensor alignment and PID values.

📦 Final Notes

Congratulations! You've now built a professional-grade PID line follower. Experiment with 5-sensor versions, analog sensors, or even Bluetooth control for next-level upgrades.

Tip: For affordable components, consider MakerBazar, Robu.in, or ElectronicsComp instead of Amazon/Flipkart. They’re cheaper but might take 7–15 days for delivery.